True the Taiwanese specimen are in general much heavier and bigger, but
it is definitely the same species. Even in the Philippines size and
thickness of the shell varies with the locality. Tibia martinii is a
deep water species and rare - try to find one yourself.  However, with
the many super fisherman they get them out of the depths occasionally
and in general in quantities. The supply is irregular. Gems are one out
of a dozen - very often growth lines etc...
You can obtain a Taiwanese shell from old collections - I do not know
about recent catches from there. Very often the Taiwanese shells have
this black deposit on them.

Guido
www.conchology.be


On 04 Jan 2005, at 08:25, Andrew Grebneff wrote:

>> I have specimens from both the Philippines (very thin, the "standard"
>> Tibia
>> martinii) and from the South China Sea (very thick and heavy, like T.
>> curta).  The two are quite different and I had planned on one day
>> doing an
>> article on them.  In the mean time, here are some measurements taken
>> of the
>> two shells that highlight just how different they are.
>>
>> South China Sea (deep water)
>> 151mm total length
>> 3mm outer lip thickness
>> 1.5mm thickness inside lip
>> 34.5 grams total weight
>> No white subsutural band
>> Weak purple banding
>> Seven outer lip digits
>> Moderately deep spiral cording
>> Unevenly tapered teleoconch
>>
>> Philippines (deep water)
>> 116mm total length
>> 1mm outer lip thickness
>> .05mm thickness inside lip
>> 7.2 grams total weight
>> White subsutural band
>> Strong purple banding
>> Five outer lip digits
>> Shallow spiral cording
>> Evenly tapered teleoconch
>>
>> As you can see, the South China Sea specimen is almost five times as
>> heavy
>> as the Philippine shell and has a much thicker shell.  The Philippine
>> shell
>> is extremely thin and feels almost like a common garden snail, Helix
>> aspersa
>> (or whatever the most recent name is).  I also have comparison
>> photographs
>> if anyone is really interested.
>>
>> Tom Eichhorst in New Mexico where it is snowing tonight.
>
> This sounds very much as though they were two species. How consistent
> are the differences? Comments, Gijs?
>
> How do I go about obtaining one of the heavy shells?
> --
> Andrew Grebneff
> Dunedin
> New Zealand
> Fossil preparator
> <[log in to unmask]>
> Seashell, Macintosh, VW/Toyota van nut
>
> ----------------------------------------------------------------------
> [log in to unmask] - a forum for informal discussions on molluscs
> To leave this list, click on the following web link:
> http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1
> Type your email address and name in the appropriate box and
> click leave the list.
> ----------------------------------------------------------------------

----------------------------------------------------------------------
[log in to unmask] - a forum for informal discussions on molluscs
To leave this list, click on the following web link:
http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1
Type your email address and name in the appropriate box and
click leave the list.
----------------------------------------------------------------------